CMP compositions and methods for polishing nickel phosphorous surfaces

ABSTRACT

Chemical mechanical polishing (CMP) compositions and methods for planarizing a nickel phosphorus (NiP) substrate are described. A NiP CMP method comprises abrading a surface of the substrate with a CMP composition. The CMP composition comprises a colloidal silica abrasive suspended in an aqueous carrier having a pH of less than 2, and containing a primary oxidizing agent comprising hydrogen peroxide, a secondary oxidizing agent comprising a metal ion capable of reversible oxidation and reduction in the presence of NiP and hydrogen peroxide, a chelating agent, and glycine. The chelating agent comprises two or three carboxylic acid substituents capable of chelating to the metal ion of the secondary oxidizing agent.

FIELD OF THE INVENTION

This invention relates to chemical mechanical polishing (CMP)compositions and methods. More particularly, this invention relates toCMP methods for polishing of nickel phosphorus (NiP) surfaces, e.g., forrigid disk applications.

BACKGROUND

Compositions and methods for CMP of the surface of a substrate are wellknown in the art. Polishing compositions (also known as polishingslurries, CMP slurries, and CMP compositions) for CMP of surfaces ofsemiconductor substrates (e.g., for integrated circuit manufacture)typically contain an abrasive, various additive compounds, and the like.Compositions for polishing nickel phosphorus (NiP) surfaces in rigiddisk (hard drive) manufacture are known in the art. Such compositionstypically utilize a silica or alumina abrasive, a primary oxidizingagent (e.g., hydrogen peroxide) and a secondary oxidizing agent (e.g.,ferric ion).

In conventional CMP techniques, a substrate carrier or polishing head ismounted on a carrier assembly and positioned in contact: with apolishing pad in a CMP apparatus. The carrier assembly provides acontrollable pressure to the substrate, urging the substrate against thepolishing pad. The pad and carrier, with its attached substrate, aremoved relative to one another. The relative movement of the pad andsubstrate serves to abrade the surface of the substrate to remove aportion of the material from the substrate surface, thereby polishingthe substrate. The polishing of the substrate surface typically isfurther aided by the chemical activity of the polishing composition(e.g., by oxidizing agents, acids, bases, or other additives present inthe CMP composition) and/or the mechanical activity of an abrasivesuspended in the polishing composition. Typical abrasive materialsinclude silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide,and tin oxide.

U.S. Pat. No. 6,015,506 discloses a polishing composition includingsilica or alumina, an oxidizer (either H₂O₂ or potassiumperoxymonosulfate) and a metal catalyst such as ferric nitrate in watersolution at pH 2 to 7. This patent speculates that the use of additivessuch as phosphoric acid or an organic acid may reduce the oxidizerdecomposition rate, but also may adversely affect the NiP removal rate.U.S. Pat. No. 6,280,490 discloses a polishing composition including anabrasive such as silica or alumina, a peroxydisulfate-based oxidizer anda ferric salt such as ferric nitrate, ferric sulfate or a ferric complexsalt such as iron (III) citrate and iron (III) EDTA in water at pH 2 andgreater. However, there is no teaching regarding the oxidizer andremoval rate stability. The slurries of U.S. Pat. No. 6,280,490 thatcontained complexed iron salts afforded lower removal rates than thosewith non-complexed iron salts, although the comparison was made atdifferent pH values. U.S. Pat. No. 6,309,434 discloses a polishingcomposition including silica as the abrasive, H₂O₂ as the oxidizer,ferric nitrate as a “polishing accelerator” and citric acid as astabilizer, at a pH of greater than 2. U.S. Pat. No. 6,309,434 assertsthat citric acid has an advantageous stabilizing effect compared toother stabilizers such as oxalic acid and malonic acid; however, thisconclusion was based on results obtained without pH adjustment fordifferent stabilizers for comparison at the same pH.

In order to improve manufacturing throughput for cost of ownership (CoO)reduction, high removal rate continues to be one of the top requirementsfor a first step NiP CMP slurry in the hard disk industry. Addition offerric salts such as ferric nitrate in CMP slurry composition are knownto improve removal rates due to the catalytic effect of the Fe³⁺ ion onNiP oxidation when combined with primary oxidizers such as hydrogenperoxide and persulfate salts. However, the presence of ferric ion cancause fast decomposition of peroxy-based oxidizers and therefore resultin unstable compositions and erratic polishing performance. Whilechelating agents (chelators) with high ferric ion binding constants,such as ethylenediaminetetraacetic acid (EDTA) andN-(hydroxyethyl)ethylenediaminetriacetic acid (HEDTA), may help tosignificantly inhibit the rapid catalytic decomposition ofperoxy-oxidizers, such chelators typically reduce the polishing removalrates at the same time. As a consequence, there is an ongoing need forcompositions and methods that can improve oxidizer stability withoutsignificantly compromising NIP material removal rates for ferricion-catalyzed CMP slurries. The compositions and methods describedherein addresses this need.

SUMMARY OF THE INVENTION

Chemical mechanical polishing compositions and methods for planarizingor polishing a nickel phosphorus (NiP) substrate are described herein.In one embodiment, a CMP method comprises abrading a surface of thesubstrate with a CMP composition. The CMP composition comprises aparticulate abrasive suspended in an aqueous carrier having a pH of lessthan 2 (preferably less than 1.5), and containing an oxidizing agent, ametal ion catalyst capable of reversible oxidation and reduction in thepresence of NiP and the oxidizer, a catalyst stabilizing agent, and a Nicomplexing agent. The catalyst stabilizing agent comprises two or threecarboxylic acid substituents capable of chelating to the metal ioncatalyst. Preferably, the abrading is accomplished in conjunction with apolishing pad in a CMP polishing apparatus.

In some method embodiments, the components of the compositionindependently are present, at point of use, at concentrations of about 1to about 20 percent by weight (wt. %) for the particulate abrasive;about 1 to about 1000 parts-per-million (ppm) for the metal ioncatalyst; about 0.3 to about 3 wt % for the oxidizing agent; about 0.001to about 2 wt % for the catalyst stabilizing agent, and optionally,about 0.3 to about 6 wt % for the Ni complexing agent.

In another aspect, a CMP composition suitable for planarizing a NiPsubstrate comprises a particulate abrasive suspended in an aqueouscarrier having a pH of less than 2, and containing a metal ion catalystcapable of reversible oxidation and reduction in the presence of NiP andthe oxidizing agent (e.g., ions of iron, cobalt, copper, europium,manganese, tungsten, molybdenum, rhenium and iridium; preferably ironand preferably Fe³⁺), a catalyst stabilizing agent, and Ni complexingagent. The stabilizing agent comprises two or three carboxylic acidsubstituents (e.g., oxalic acid, citric acid, malonic acid) capable ofchelating to the metal ion catalyst.

In some CMP composition embodiments, the components of the compositionindependently are present at concentrations of about 1 to about 50percent by weight (wt %) for colloidal silica; about 1 to about 2500parts-per-million (ppm) for the metal ion catalyst; about 0.3 to about.7.5 wt % for the oxidizing agent; about 0.001 to about 5 wt % for thestabilizing agent; and about 0.3 to about 15 wt % for the Ni complexingagent. The oxidizing agent generally is added to the composition shortlybefore use (e.g., a few hours before).

The compositions and methods described herein are particularly useful inplanarization of NiP substrates for rigid disk applications, andsurprisingly provide improved composition stability at very low pH(e.g., less than about 2) while maintaining commercially suitable NiPremoval rates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a graph of H₂O₇ concentration versus tunic in hours (potlife) at different Fe ion concentrations.

FIG. 2 provides a graph of H₂O₂ concentration versus time for differentstabilizer types and concentrations.

FIG. 3 provides a graph of removal rate vs. pot life for differentstabilizer types and concentrations.

FIG. 4 provides a graph of H₂O₂ concentration versus time for differentpH values and stabilizers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Chemical mechanical polishing compositions and methods described hereinutilize a slurry comprising a particulate abrasive suspended in anaqueous carrier having a pH of less than 2 an oxidizing agent, a metalion catalyst capable of reversible oxidation and reduction in thepresence of NiP and the oxidizing agent, a Ni complexing agent, and acatalyst stabilizing agent.

The catalyst stabilizing agent comprises two or three carboxylic acidsubstituents capable of chelating to the metal ion catalyst.Non-limiting examples of suitable stabilizing agents include oxalicacid, malonic acid, succinic acid, malic acid, tartaric acid, citricacid, glutaric acid, adipic acid, maleic acid, phthalic acid andiminodiacetic acid. In some embodiments, the chelating agent is selectedfrom oxalic acid, citric acid, malonic acid, and a combination of two ormore thereof. As used herein the terms “carboxylic acid” and “acid” asused in reference to stabilizing agents are meant to encompass the freeacid form as well as salts (e.g., alkali metal salts). Preferably, thechelating agent is present at a concentration of about 0.001 to about 2wt % at point of use, more preferably about 0.03 to about 0.4 wt %,e.g., about 0.04 to about 0.2 wt %, and preferably are present at amolar concentration of 2 or more times the molar concentration of themetal ion catalyst (e.g., 2 to 20 times the metal ion molarconcentration, preferably about 2 to 10, or 2 to 5 times the metal ionmolar concentration).

Without wishing to be bound by theory, it is believed that the Nicomplexing agent in the polishing slurry aids in Ni removal bycomplexing with nickel ions formed during the polishing process.Preferably, the Ni complexing agent is an amino acid or carboxylic acid.Non-limiting examples of possible Ni complexing agents include glycine,alanine, aspartic acid, histidine, nitriloacetic acid, iminodiaceticacid, acetic acid, tartaric acid, citric acid, oxalic acid, lactic acid,glutaric acid, maleic acid, gluconic acid, malonic acid and glycolicacid. Preferably, the Ni complexing agent is glycine. Preferably, the Nicomplexing agent is present in the composition at a concentration ofabout 0.3 to about 6 wt %, e.g., about 0.3 to about 1 wt %, at point ofuse.

The metal ion catalyst is capable of reversible oxidation and reductionin the presence of NiP and an oxidizing agent (e.g., hydrogen peroxide).Any suitable metal ion catalyst may be used. Preferred metal ionsinclude ions of iron, cobalt, copper, europium, manganese, rhenium,molybdenum, iridium and tungsten. Non-limiting examples of such metalions include Fe²⁺, Fe³⁺, Co²⁺, Cu²⁺, Eu³⁺, Mn²⁺, W⁶⁺, Re⁷⁺, Mo⁵⁺ andIr³⁺. Preferably, the metal ion is or comprises Fe³⁺. Typically, themetal ion is included in the CMP composition as a soluble salt, forexample, a nitrate, a halide (e.g., chloride), a sulfate, and the like.Optionally, the metal ion can be included in the slurry as a salt withthe stabilizing agent, e.g., a malonic acid salt, citric acid salt, andthe like.

The metal ion catalyst is, preferably, present in the composition (atpoint of use) at a concentration of greater than about 1 ppm (e.g.,about 5 ppm, about 10 ppm, about 20 ppm, about 50 ppm, about 100 ppm).The metal ion catalyst is, preferably, present in the composition (atpoint of use) at a concentration of less than about 1000 ppm (e.g.,about 750 ppm, about 500 ppm, about 250 ppm, about 150 ppm, about 125ppm). The metal ion catalyst may be present in the composition (at pointof use) at a concentration range bounded by any of the aforementionedconcentrations, for example, about 1 to about 1000 ppm, preferably about20 to about 250 ppm, e.g., about 50 to about 150 ppm.

The oxidizing agent comprises, consists essentially of, or consists ofhydrogen peroxide, optionally in combination with periodic acid, or aperoxy-based oxidizer such as a peroxymonosulfate or peroxydisulfatesalt. The inventive CMP composition comprises, at point of use, aconcentration of the oxidizing agent of about 0.1 wt. % or greater(e.g., about 0.2 wt. %, 0.3 wt. %, 0.5 wt. %, 0.7 wt. %). Theconcentration of the oxidizing agent may be about 4.0 wt. % or less(e.g., about 3 wt. %, about 2.5 wt. %, about 2 wt. %, about 1.8 wt. %,about 1.5 wt. %, about 1.25 wt. % about 1 wt. %), The concentration ofoxidizing agent may within the range bounded by any two of the foregoingendpoints. For example, the concentration range of the oxidizing agentmay be, without limitation, about 0.3 wt. % to about 3 wt. %, about 0.2wt. % to about 2.5 wt. %, about 0.3 to about 1.8 wt. %, of the oxidizingagent (e.g., hydrogen peroxide).

The particulate abrasive can comprise any abrasive material suitable foruse in CMP of memory or rigid disk substrates, semiconductor, andintegrated circuit materials. Examples of such materials include, e.g.,silica, ceria, alumina, zirconia, and titania. A preferred particulateabrasive comprises, consists essentially of or consists of silica (e.g.,colloidal silica). In some embodiments, a mixed abrasive systemcomprising e.g., alumina and silica can be utilized. The abrasive may beof any suitable particle size. Preferably, the particulate abrasive hasa mean particle size of about 4 to about 500 nm. Colloidal silica is apreferred abrasive material.

The compositions of the present invention have a pH of less than 2,preferably a pH of less than 1.8, preferably a pH of less than 1.5(e.g., a pH of about 1 to about 1.8, a pH of about 1 to about 1.5). ThepH of the composition can be achieved and/or maintained by inclusion ofan acidic buffering material if desired. Acidic buffers are well knownto those of ordinary skill in the chemical arts.

The polishing compositions described herein optionally also can includesuitable amounts of one or more other additive materials commonlyincluded in polishing compositions, such as dispersants, viscositymodifying agents, biocides, nonionic surfactants, and the like. Forexample, the composition can include a biocide such as KATHON or NEOLONEbiocides. In some preferred embodiments, the CMP composition is freefrom viscosity modifying agents such as carboxymethylcellulose, and thelike.

The aqueous carrier can be any aqueous solvent, e.g., water, aqueousmethanol, aqueous ethanol, a combination thereof, and the like.Preferably, the aqueous carrier comprises predominately water (e.g.,deionized water).

The polishing compositions used in the methods described herein can beprepared by any suitable technique, many of which are known to thoseskilled in the art. The polishing composition can be prepared in a batchor continuous process. Generally, the polishing composition can beprepared by combining the components thereof in any order. The term“component” as used herein includes individual ingredients (e.g.,abrasive, catalyst stabilizing agent, metal ion catalyst, Ni complexingagent, buffers, oxidizing agent, and the like), as well as anycombination of ingredients. For example, the abrasive can be dispersedin water, combined with the metal ion catalyst, catalyst stabilizingagent, and Ni complexing agent components, and mixed by any method thatis capable of incorporating the components into the polishingcomposition. Typically, the oxidizing agent is not added to the CMPcomposition until the composition is ready for use in a CMP process, forexample, the oxidizing agent can be added shortly before initiation ofpolishing. The pH can be further adjusted at any suitable time byaddition of an acid or base, as needed.

The polishing compositions of the present invention also can be providedas a concentrate, which is intended to be diluted, with an appropriateamount of aqueous solvent (e.g., water) prior to use. In such anembodiment, the polishing composition concentrate can include thevarious components dispersed or dissolved in aqueous solvent in amountssuch that, upon dilution of the concentrate with an appropriate amountof aqueous solvent, each component of the polishing composition will bepresent in the polishing composition in an amount within the appropriaterange for use.

The compositions and methods of the invention surprisingly provideenhanced oxidizer stability while still affording commercially suitableremoval rates when polishing a NiP surface. Without intending to bebound by theory, we have discovered that in order to achieve significantNiP removal rates while maintaining stability of the oxidizing agent(e.g., hydrogen peroxide), the pH of a polishing slurry should be highlyacidic (e.g., pH less than about 2, preferably less than about 1.5),while the combination of the catalyst stabilizing agent with the Nicomplexing agent, stabilize the oxidizer and aid in nickel ion removalfrom the substrate.

The CMP methods of the invention preferably are achieved using achemical-mechanical polishing apparatus. Typically, the CMP apparatuscomprises a platen, which, when in use, is in motion and has a velocitythat results from orbital, linear, and/or circular motion, a polishingpad in contact with the platen and moving relative to the platen when inmotion, and a carrier that holds a substrate to be polished bycontacting and moving relative to the surface of the polishing pad. Thepolishing of the substrate takes place by the substrate being placed incontact with the polishing pad and a polishing composition of theinvention and then moving the polishing pad relative to the substrate soas to abrade at least a portion of the substrate to polish thesubstrate.

The following examples further illustrate certain aspects of theinvention but, of course, should not be construed as in any way limitingits scope. As used herein and in the following examples and claims,concentrations reported as parts-per-million (ppm) or percent by weight(wt. %) are based on the weight of the active component of interestdivided by the weight of the composition.

General Experimental Procedure

All NiP disks were polished using a 6EE DOUBLE SURFACE POLISHMETER (fromStrasbaugh, San Jose, Calif.). Twenty five disks were polished in eachrun at a slurry flow rate of about 400 mL/min with a CR200 polishing,pad (from Ceiba Technologies, Chandler Ariz.), at a down force of about130 kg, an upper platen speed of about 20 revolutions-per-minute (rpm),a lower platen speed of about 30 rpm, and a carrier speed of about 5rpm. Weight measurements were made on five disks to determine thematerial removal rates (RR, in mg/min). The slurries comprised (a)abrasive (variable amounts); (b) hydrogen peroxide (variable amounts);(c) metal ion catalyst (variable amounts); (d) Ni complexing agent(variable amounts); (e) catalyst stabilizing agent. (variable amounts);and (f) nitric acid (variable amounts for pH adjustment). As usedherein, “variable amounts” refers to varying amount and identity of thespecified component, and in some cases, the absence of the specifiedcomponent in the slurry composition.

Example 1

Different carboxylic acids and amino acids were screened as Nicomplexing agents for comparison. The polishing was performed at aboutpH 1.8 with 5 wt % colloidal silica (“Silica A”, colloidal silica havinga surface area about 80 m²/g (by titration) and a mean particle size of40 nm, based on manufacturer information), 0.6 wt % hydrogen peroxide,with no metal ion catalyst, and no catalyst stabilizing agent. Thepolishing results shown in Table 1 show that the presence of a Nicomplexing agent significantly improves the removal rate, with bestcomplexing agent being glycine. Results of additional evaluations ofglycine at different concentrations, with and without a metal ioncatalyst, and with different silica type and loading are found in Table2, which demonstrates that a glycine concentration of about 0.65 wt %provided the best performance.

TABLE 1 Ni complexer RR Slurry (87 mM) (mg/min) S1 Tartaric acid 12.78S4 citric acid 10.2 S5 oxalic acid 13.54 S1 Tartaric acid 12.61 S1Tartaric acid 12.4 S2 Lactic acid 11.77 S3 Glutaric acid 13.38 S4 Maleicacid 13.46 S5 Gluconic acid 12.81 S6 Malonic acid 12.22 S7 Glycolic acid13.41 S8 — 9.96 S1 Tartaric acid 12.67 S1 Tartaric acid 13.54 S2 Glycine17.39 S3 Alanine 13.8 S4 Aspartic acid 14.26 S5 Histidine 13.44 S6Nitriloacetic acid 12.67 S7 Iminodiacetic acid 14.42 S11 acetic acid12.99 S1 Tartaric acid 13.15

TABLE 2 Silica Glycine RR Slurry (wt % solids) Fe (ppm) (wt %) pH(mg/min) S2A A (5%) 0 0.3 1.8 11.88 S3A A (5%) 0 0.65 1.8 15.29 S4A A(5%) 0 1 1.8 13.65 S5A A (5%) 0 2 1.8 10.06 S1B B (3%) 50 0.65 1.3 21.41S2B B (3%) 50 0.75 1.3 19.56 S3B B (3%) 50 0.55 1.3 21.3 S1B B (3%) 500.65 1.3 23.07

In Table 2, Silica “A” is colloidal silica having a surface area ofabout 80 m²/g (by titration) and a mean particle size of about 40 nm,and Silica “B” is colloidal silica having a surface area of about 80m²/g (by titration) and a mean particle size of about 34 nm, based onpublished information.

Example 2

This Example demonstrates the effect of a metal ion catalyst in apolishing NiP substrate. Table 3 illustrates the effect of ironconcentration, demonstrating an increasing trend of removal rate withincreasing iron content at the to 100 ppm range. Evaluations were run atpH 1.3, with 0.6 wt % hydrogen peroxide, 0.6 wt % glycine, and 3 wt % ofcolloidal silica B). For instance, a slurry with 50 ppm of Fe³⁺ (asFe(NO₃)₃) exhibited a 1.4% improvement in removal rate compared to aslurry without any metal ion catalyst. Table 4 illustrates a similarremoval rate improvement effect of Fe(NO₃)₃ for a mixed abrasive system(fumed alumina, colloidal alumina, and colloidal silica). Evaluations inTable 4 were run with 1.2 wt % hydrogen peroxide, 0.8 wt % tartaric acid(as a Ni complexing agent), and 108 ppm of an ethoxylated-propoxylatedsilicone block copolymer surfactant (SILWET 7200 approximate ratio ofsilicone-to-ethylene oxide-to-propylene oxide of about 35:40:25, basedon manufacturer information) at pH 1.8. A number of other metal salts asmetal ion catalysts (listed in Table 5) were found to have comparable,or slightly less, removal rate improvement when compared to Fe(NO₃)₃,including cobalt (II) nitrate copper (II) nitrate, europium (III)nitrate, manganese (II) nitrate, tungsten (VI) chloride, molybdenum (V)chloride, iridium (III) chloride and methyl trioxorhenium (VII).Evaluations in Table 5 were run with 1.2 hydrogen peroxide, 3 wt %Silica B, and 0.6 wt % glycine, at pH 1.3, with the metal ion catalystsat the same molar concentration of 50 ppm Fe from ferric nitrate.However, because these compositions did not contain the catalyststabilizing agent, titration results shown in FIG. 1 demonstrates thatthe H₂O₂ decomposition rate increased dramatically with an increasemetal ion catalyst content.

TABLE 3 Slurry Fe (ppm) RR (mg/min) S1C 50 27.06 S4C 0 23.88 S5C 7527.97 S6C 100 32.54 S1C 50 27.43

TABLE 4 Particles (wt % solids) Fe (ppm) Fe complexer (%) RR (mg/min)α-Alumina (0.525%) + 0 — 26.78 Fumed alumina (0.131%) + Silica A (1.97%)α-Alumina (0.525%) + 100 Malonic acid 31.44 Fumed alumina (0.131%) +(0.0931%) Silica A (1.97%)

TABLE 5 Catalyst (equivalent molar Slurry to 50 ppm Fe) RR (mg/min) S1DIron (III) Nitrate 20 S4D Cobalt (II) Nitrate 18.4 S1D Iron (III)Nitrate 20.3 S6D Copper (II) Nitrate 18.7 S7D Europium (III) Nitrate19.7 S8D Manganese (II) Nitrate 19.4 S9D Tungsten (VI) Chloride 18.7S10D Molybdenum (V) Chloride 17.5 S11D Iridium (III) Chloride 20.1 S12DMethyltrioxorhenium (VII) 19.9 S1D Iron (III) Nitrate 18.3

Example 3

Different catalyst stabilizing agents were evaluated to assess theimpact on peroxide decomposition and polishing performance. Table 6lists catalyst stabilizing agents and concentration for slurriesevaluated using Silica B (3 wt %)+Silica A (7 wt %), wt % hydrogenperoxide, 100 ppm of ferric ion as the metal ion catalyst, and 0.6 wt %glycine as the Ni complexing agent, at pH 1.5. The corresponding potlife results (in terms of H₂O₂ concentration) are shown in FIG. 2. Bothoxalic acid and malonic acid exhibited a good stabilizing effect. Theresults show that the higher the stabilizer concentration, the slowerthe H₂O₂ decomposition. At the same molar concentration, oxalic acidprovided a better stabilizing effect than malonic acid, likely due to astronger complexation with iron. The polishing results, shown in FIG. 3,demonstrated a similar stability trend in terms of removal rate, in thatboth oxalic acid and malonic acid significantly reduced the removal ratedrop over a 48-hour pot life. While oxalic acid leads to lower peroxidedecomposition than malonic acid, it also reduced the fresh pot removalrate (Day 0) compared to a slurry without any stabilizer (S1E). On thecontrary, malonic acid (S9E and S10E) surprisingly exhibited no suchcompromise on fresh pot removal rate.

TABLE 6 Fe chelator Slurry (concentration) S1E — S4E Oxalic acid(0.0806%) S5E Oxalic acid (0.0403%) S6E Oxalic acid (0.0161%) S8EMalonic acid (0.0186%) S9E Malonic acid (0.0559%) S10E Malonic acid(0.0931%)

Example 4

A study was carried out to compare the methods of the present inventionto those of patent U.S. Pat. No. 6,309,434, where it was reported thatcitric acid provided a better stability than malonic acid. Details ofthe slurry compositions tested in this example are provided in Table 7,Evaluations were run with 15 wt % Silica B, 3 wt % hydrogen peroxide,400 ppm of ferric nitrate with the catalyst stabilization agent, pHadjustor, and PH shown in Table 7, but without glycine. Slurries No S5Fand No S7F are the same composition as Slurries No. S4F and S6F,respectively, but without pH adjustment (i.e., as in U.S. Pat. No.6,309,434). The polishing results in Table 7 demonstrate that citricacid provided a better removal rate than malonic acid at pH 2.6 to 2.7(comparative example); however, when the pH was adjusted down to about1.3 as described herein, malonic acid provided a better removal ratethan citric acid. A one-week pot life study revealed that higher pHprovided better stability for both stabilizers, likely due to betterstabilizer coordination to the metal ion catalyst, Fe³⁺. Malonic acidafforded a better removal rate stability (i.e., consistency of theremoval rate over time) than citric acid at pH 1.3, while the two acidswere about equally effective in stabilizing the removal rate at pH 2.6to 2.7. The corresponding titration result in FIG. 4 reveals thatmalonic acid provided a better H₂O₂ stability than citric acid at bothpH 1.3 and at pH 2.6 to 2.7. This result is opposite to the observationsreported in U.S. Pat. No. 6,309,434.

TABLE 7 Stabilizing RR @ 0 RR @ 166 Agent pH ad- hr pot life hr pot lifeSlurry (concentration) justor pH (mg/min) (mg/min) S4F Citric acid(0.4%) HNO₃ 1.3 17.36 15.95 S5F Citric acid (0.4%) no ad- 2.7 13.3713.87 justment S6F Malonic acid HNO₃ 1.3 17.99 17.55 (0.2%) S7F Malonicacid no ad- 2.6 10.9 11.18 (0.2%) justment

In summary, the inventive CMP compositions described herein (i.e.,comprising a metal ion catalyst, a Ni complexing agent, a catalyststabilization agent, an abrasive, and a peroxide-based oxidizing agent)provide enhanced material removal rates and improve removal ratestability for polishing NiP hard disk substrates. Malonic acid is thepreferred catalyst stabilizing agent for preventing peroxide degradationwithout sacrificing the removal rate, when compared to oxalic acid andcitric acid. This advantage is more significant at low pH of less than1.5 (e.g., 1.3) compared to higher pH values (e.g., pH of about 2.6 to2.7).

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

Example 5

This example demonstrates the ability of the inventive method to polishNiP substrates with and without the Ni complexing agent. This experimentwas run on a Logitech table top polisher using the following settings; 1psi downforce, 65 rpm platen speed, a slurry flow rate of 100 mL/min. ACR200 polishing pad was used (Ceiba Technologies). A separate Nickelphosphate (NiP) wafer having a composition of 12% phosphate and 88%nickel was polished for each treatment. The removal rates weredetermined by weight differential (final weight subtracted from initialweight) using an analytical balance. Because the industrial standard isto report removal rates in mg/min with a double sided polisher, theobserved removal rates for this table top experiment were doubled to beconsistent with reported rates.

The hydrogen peroxide decomposition was determined by analyzing theperoxide concentration of fresh slurry (1.2% hydrogen peroxide) and thatof the slurry after tour days at room temperature. The peroxideconcentrations were determined by titration method with potassiumpermanganate. The results are reported as the final peroxideconcentration divided by the initial (original) peroxide concentration.

The treatments all had 1.2 wt. % hydrogen peroxide, 6 wt. % silica B, atpH 1.3. The treatments, as set forth below in Table 8, had either 0.6wt. % glycine (100% glycine), a molar equivalent of malonic acid (100%malonic), or 0.3 wt. % glycine and the molar equivalent of malonic acid(50% glycine and 50% malonic).

The results shown in Table 8 indicate that removal rates increased withincreasing ferric ion concentration. However, the stability of thehydrogen peroxide was a function of the amount of malonic acid present.For example, at 1.50 ppm ferric ion concentration, the removal rateswere equivalent for the formulations having either 100% malonic or 100%glycine. The stability of the peroxide after 4 days at room temperaturedecreased from 0.904 to 0.011 for the 100% malonic and the 100% glycine,respectively. The results for the 50% malonic and 50% glycine, at 100ppm ferric iron, showed a stability of 0.836, indicating that peroxidecould be stabilized with lower concentrations of Platonic acid.

TABLE 8 [Fe] RR [H2O2]/[H2O2]o (ppm) % Malonic % Glycine (mg/min) after4 days 50 0 100 22.36 0.329 100 50 50 23.42 0.836 150 0 100 26.31 0.011150 100 0 26.11 0.904 50 100 0 22.19 1.01

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. The terms “consisting of” and“consists of” are to be construed as closed terms, which limit anycompositions or methods to the specified components or steps,respectively, that are listed in a given claim or portion of thespecification. In addition, and because of its open nature, the term“comprising” broadly encompasses compositions and methods that “consistessentially of” or “consist of” specified components or steps, inaddition to compositions and methods that include other components orsteps beyond those listed in the given claim or portion of thespecification. Recitation of ranges of values herein are merely intendedto serve as a shorthand method of referring individually to eachseparate value falling within the range, unless otherwise indicatedherein, and each separate value is incorporated into the specificationas if it were individually recited herein. All numerical values obtainedby measurement (e.g., weight, concentration, physical dimensions,removal rates, flow rates, and the like) are not to be construed asabsolutely precise numbers, and should be considered to encompass valueswithin the known limits of the measurement techniques commonly used inthe art, regardless of whether or not the term “about” is explicitlystated. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate certain aspects of the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A chemical mechanical polishing (CMP) method forplanarizing a nickel phosphorus (NiP) substrate, the method comprisingabrading a surface of the substrate with a CMP composition; the CMPcomposition comprising a particulate abrasive suspended in an aqueouscarrier having a pH of less than 1.5, and containing an oxidizing agentcomprising hydrogen peroxide, a metal ion catalyst capable of reversibleoxidation and reduction in the presence of NiP and the oxidizer, acatalyst stabilizing agent, and a Ni complexing agent, wherein the Nicomplexing agent is glycine; wherein the catalyst stabilizing agent ismalonic acid, and wherein the catalyst stabilizing agent is present inthe CMP composition at a concentration of about 0.04 to about 0.2 wt %and present in a molar concentration of 2 to 5 times the metal ion molarconcentration.
 2. The method of claim 1 wherein the metal ion catalystcomprises at least one ion selected from the group consisting of ions ofiron, cobalt, copper, europium, manganese, rhenium, molybdenum, iridiumand tungsten.
 3. The method of claim 1 wherein the metal ion catalyst isan iron ion.
 4. The method of claim 3 wherein the iron ion comprisesFe³⁺.
 5. The method of claim 1 wherein the catalyst stabilizing agent isselected from the group consisting of oxalic acid, citric acid, malonicacid, and a combination of two or more thereof; and the metal ioncatalyst comprises Fe⁺³.
 6. The method of claim 1 wherein theparticulate abrasive is colloidal silica.
 7. The method of claim 6wherein the colloidal silica is present in the CMP composition at aconcentration of about 1 to about 20 percent by weight (wt %).
 8. Themethod of claim 1 wherein the metal ion catalyst is present in the CMPcomposition at a concentration of about 50 to about 150parts-per-million (ppm).
 9. The method of claim 1 wherein the oxidizingagent is present in the CMP composition at a concentration of about 0.3to about 1.8 wt %.
 10. The method of claim 1 wherein Ni complexing agentis present in the CMP composition at a concentration of about 0.3 toabout 1 wt %.
 11. The method of claim 1 wherein the abrading isaccomplished in conjunction with a polishing pad in a CMP polishingapparatus.